1. Technical Field
The present invention relates to an imaging device using photodiodes, an electronic apparatus including the imaging device, and an imaging method using the imaging device.
2. Related Art
In a photodiode used in an imaging device, electric charge according to the amount of received light is excited during a light exposure period. In the imaging device, however, after the light exposure but before the voltage across the photodiode is read, leak current flows in the direction from the N-type impurity layer of the photodiode toward the P-type impurity layer thereof (reverse direction), and the electric charge excited in the photodiode therefore decreases. It is therefore undesirably difficult to accurately detect the amount of light received with the photodiode.
To solve the problem, JP-A-2006-216643 discloses an imaging device including a photodiode in which electric charge according to the amount of received light is excited, an amplification transistor that produces an imaging signal according to the voltage at the cathode of the photodiode, and a leak current cancellation diode connected to the cathode of the photodiode. In the imaging device, in the period for which leak current flows from the cathode of the photodiode to the anode thereof, leak current flows into the cathode of the photodiode via the leak current cancellation diode to replenish the electric charge lost due to the leak current in the photodiode.
In the technology disclosed in JP-A-2006-216643, the electric charge lost from the photodiode due to the leak current is replenished by the leak current from the leak current cancellation diode. It is therefore necessary to set the magnitude of the leak current from the photodiode to be equal to the magnitude of the leak current from the leak current cancellation diode. The characteristics of the photodiode and the leak current cancellation diode, however, vary product to product, and it is therefore difficult to set the magnitude of the leak current from the photodiode to be equal to the magnitude of the leak current from the leak current cancellation diode. Therefore, according to the technology disclosed in JP-A-2006-216643, it is difficult to acquire an imaging signal accurately representing the amount of light received with the photodiode.